> On Jan 8, 2015, at 9:11 AM, Bart Van Assche <[email protected]> wrote:
>
> On 01/08/15 14:45, Sagi Grimberg wrote:
>> Actually I started with that approach, but the independent connections
>> under a single session (I-T-Nexus) violates the command ordering
>> requirement. Plus, such a solution is specific to iSER…
The iSCSI standard specifies an ordering requirement for the case of multiple
connections under a single session. That requirement is in fact a reason why
some iSCSI targets have declined to implement multiple connections.
On the other hand, there are lots of “MPIO” implementations in many different
operating systems that use multiple sessions, so there is no ordering at the
iSCSI level, and whatever ordering is required (if any) is instead implemented
at higher layers in the requesting OS.
>
> Hello Sagi,
>
> Which command ordering requirement are you referring to ? The Linux storage
> stack does not guarantee that block layer or SCSI commands will be processed
> in the same order as these commands have been submitted.
Neither does SCSI, in fact. The ordering rules of the SCSI standard are worth
studying. They are a lot weaker than most people expect. A particularly
interesting case is multiple concurrent writes with overlapping block ranges.
paul
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